The present invention relates to a shock-absorbing feed roller and more particularly to an adjustable, resiliently carried feed roller for use in a tree-harvesting unit connected to a forest processor.
Modern logging operations are carried out with the aid of advanced logging processors, so-called harvesters, provided with a tree-harvesting unit. The harvesting unit fells, trims and cuts trees into desired lengths.
When a tree is felled, the root end of the tree trunk is held inserted between drive wheels or feed rollers which clamp around the trunk on opposite sides thereof. The trunk is then trimmed by feeding the trunk through the harvesting unit with the aid of the feed rollers, the harvesting unit comprising appropriately disposed knives for removing knots, branches, etc., from the trunk. In order to achieve a fully satisfactory trimming result, it is important that the feed rollers grip the trunk satisfactorily. It is known to provide the feed rollers with studs, teeth, ribs or like gripping means which are intended to penetrate through the bark and grip or bite into the surface wood of the log, so as to eliminate the risk of the rollers slipping as bark is loosened from the surface wood. The force with which the feed roller engages the log is also important in achieving a satisfactory grip.
The feed rollers thus operate with forces that act both radially, i.e. grip-improving clamping forces against the trunk, and forces which act peripherally, i.e. feed forces generated by the torque of the drive arrangement.
An early known feed roller or feed wheel is manufactured totally from steel and is provided around its outer surface with studs or ribs which are intended to penetrate through the bark on the log so as to achieve a better grip in the surface wood of the log. The drawback with this feed wheel is that it is rigid and non-resilient, such that the wheel, or roller, will strike against the trunk with considerable force as the wheel passes irregularities along the surface of the trunk. This drawback is the result of the high clamping forces with which the feed wheels are engaged with the trunk and that are required in order to obtain a satisfactory grip, and because of the inability of the feed wheels to absorb impacts. The impact of the inelastic and rigid wheel against the tree trunk results in damage to the surface wood, which, in turn detracts from the price that can be demanded for the harvested timber. Notwithstanding this, however, this latter type of feed wheel has the advantage of a long useful life.
A feed wheel used at present includes a steel hub on which a rubber covering or rubber tread is affixed by vulcanization. This feed wheel has a gentler effect on the trunk, since the rubber tread functions to absorb shocks and impact forces as the wheel strikes against the trunk. The rubber-covered wheels are normally provided with chain-type grippers, so as to obtain an effective grip with the trunk. However, a feed wheel that has a rubber covering has a much shorter useful life than a wheel that has a steel outer periphery. Furthermore, in the case of a rubber-covered wheel, it is necessary to dismantle the entire wheel in order to replace the rubber covering or rubber tread, a task which normally has to be carried out on factory premises.
A forest processor normally works over large areas of forest and is liable to come into contact with several different types of trees. This means that the properties of the wood and of the bark are also liable to vary, therewith requiring the feed rollers, or wheels, to be adaptable to relevant requirements. At present, it is not possible to vary the resilient properties of feed rollers or feed wheels in a quick and simple fashion, or to vary the design of the gripping elements and their sizes, etc.